purespace-write-error

Lisp can have a pll file where constant strings and codevectors
can be stored, thus saving space in the Lisp heap and avoiding
duplicate strings and
codevectors. See Creating and using pll files
in miscellaneous.htm for details. Constant strings
stored in a pll cannot be modified. Doing so signals an error
of condition type purespace-write-error, as the following
example shows (run in a modern Lisp where Common Lisp symbols are
named with lowercase strings -- see case.htm):